JP-2002-23761A discloses a drive circuit connected to a sound generating body and having an error determination circuit for detecting an open-circuit in the sound generating body. The error determination circuit measures a current and a voltage of a magnetic coil of the sound generating body.
JP-2003-274491A discloses an open-circuit detection device for detecting an open-circuit in a speaker. The open-circuit detection device includes an equivalent circuit having equivalent impedance to the speaker circuit and detects the open-circuit by comparing an impedance of the equivalent circuit with an impedance of the speaker circuit.
JP-2007-37024A discloses a speaker line testing device for detecting an open-circuit and a short-circuit in a speaker circuit by measuring an impedance of the speaker circuit.
JP-2011-70561A discloses an alarm device including a switch. The switch connects a circuit, which supplies a detection voltage used for open-circuit detection in a piezoelectric sound generating body, to the sound generating body, only when the open-circuit detection is performed.
The error determination circuit disclosed in JP-2002-23761A includes a current transformer and a voltage transformer on a line connected to the sound generating body. Therefore, it is difficult to reduce the number of parts, the size, and the cost of the error determination circuit.
The open-circuit detection device disclosed in JP-2003-274491A includes the equivalent circuit and a switch circuit. Therefore, it is difficult to reduce the number of parts, the size, and the cost of the open-circuit detection device. Further, the open-circuit detection device cannot detect a failure such as an open-circuit during normal operation.
The testing device disclosed in JP-2007-37024A includes a detection circuit for detecting a current in a speaker line. Therefore, it is difficult to reduce the number of parts, the size, and the cost of the testing device. Further, in the testing device, an alternating current (AC) signal of an inaudible frequency range is mixed with an audible signal. Therefore, the testing device requires an AC signal generator. Further, in the testing device, a mixed signal of the audible signal and a test signal needs to be amplified.
In the alarm device disclosed in JP-2011-70561A, the detection voltage is supplied only when the detection is performed. Therefore, the alarm device cannot detect a failure such as an open-circuit during normal operation.